1. Field of the Invention
The present invention relates in general to traffic signs which issue traffic signals for achieving the safety passage of motor vehicles running on roads, and more particularly to traffic signs of a type which is mounted on a paved road. More specifically, the present invention is concerned with the traffic signs of a type having a sinkable light source for protecting the light source when a snow removing vehicle or the like runs over the sign.
2. Description of the Prior Art
Hitherto, various types of traffic signs of the above-mentioned type have been proposed and put into practical use.
For clarifying the task of the present invention, exemplified two of the conventional traffic signs of such type will be briefly described in the following.
One is a traffic sign described in Japanese Patent Second Provisional Publication 59-122612, which will be described with reference to FIGS. 12 and 13 of the accompanying drawings.
As is seen from FIG. 12, the traffic sign of the publication comprises a bottomed cylindrical housing 1 which is laid under a paved road surface "r". A circular elastic member 2 is put on the bottom of the housing 1 and a projected member 3 is put on the circular elastic member 2. A reflector holder 4 constructed of a transparent material is mounted on the projected member 3. The reflector holder 4 comprises a flat bottom wall 4a and a convex upper wall 5 which is integrally projected from a periphery of the flat bottom wall 4a. As shown, the convex upper wall 5 is projected upward beyond the paved road surface "r" and has a plurality of light reflecting plates 6 embedded in a slanted wall part 5a of the wall 5. An elastically deformable annular gasket 7 is arranged with its inner peripheral portion resiliently disposed between the projected member 3 and the flat bottom wall 4a of the reflector holder 4.
When now as is seen from FIGS. 12 and 13, a snow removing vehicle running on the road surface "r" comes to a position to have its snow removing blade 8 collide against the convex upper wall 5, the convex upper wall 5 becomes sunken due to the flexibility possessed by the annular gasket 7 and the compressibility possessed by the circular elastic member 2. After the snow removing blade 8 passes through the convex upper wall 5, the upper wall 5 is returned back to its projected normal position due to the return force of the gasket 7 and the elastic member 2. In this normal position of the convex upper wall 5, the light reflecting plates 6 can be viewed from the road surface "r". Due to the vertical mobility of the convex upper wall 5, undesired breakage of the same is avoided.
The other is a traffic sign described in Japanese Patent Second Provisional Publication 9-158135. In the sign of this publication, a biasing spring is used for biasing a light reflector upward. That is, when the snow removing vehicle runs on the light reflector, the light reflector is moved down against the biasing force of the spring. Once the vehicle passes through the light reflector, the reflector is moved up to its projected normal position.
However, even the above-mentioned two traffic signs have failed to exhibit satisfied performance due to their inherent constructions. That is, in the former sign, the convex upper wall 5, especially, the slanted wall part 5a of the same tends to loose its transparency due to repeated attacks by snow removing vehicles. If the transparency is severely lowered, the light reflecting plates 6 can not effectively reflect a light. In the latter sign, the biasing spring tends to loose its resiliency due to the repeated compression and expansion movements.